INDUSTRY FOCUS CABLES & CONNECTORS
UNDERSTANDING CABLE MANAGEMENT MATERIALS
S
pecifying the correct cable management for different environments can be a
minefield that even experienced electrical consultants, engineers and contractors struggle to navigate effectively. Not only do you need to make basic decisions about whether cable ladder, cable tray, cable basket or cable trunking offers the most appropriate solution for each element of the build, you also need to select the right size (width and depth), the right weight (heavy, medium or standard duty) and the right material or finish. That is before we even get into any discussion of the difference between individual systems and their practical and commercial benefits. Indeed, the number of variables is so extensive that there should never be a one- size-fits-all or copy-and-paste approach to cable management specification. Far from being a commodity item, it is actually the backbone of any electrical installation and correct specification that will determine the durability and longevity of the installation.
ENVIRONMENTAL FACTORS The starting point for selecting the right cable management materials must be consideration of the environmental factors affecting each element of the project. For example, is the cable management required indoors where it will be protected from the elements? Or outdoors where it will be exposed? If it is going to be indoors, will the atmosphere be clean or polluted? And if it is going to be outdoors, will it be inland or in a coastal or marine location where a saline atmosphere is a factor? As standard cable management systems
are usually pre-galvanised or hot-dip galvanised steel, it is important to understand corrosion risk categories for zinc. There are six categories in all, ranging from C1 (very low), which would typically be inside an insulated building with relative humidity <60 per cent, where zinc loss in the first year would be measured at <0.1µm. The scale rises to C5I (very high industrial) where the system is installed in an external environment with considerable humidity and an aggressive atmosphere, or an interior location with almost constant water condensation and high levels of pollution or C5M (very high maritime) for coastal areas with high salinity and anticipated 1st year zinc loss of 4.2 - 8.4µm. For indoor environments it should be simple to understand the conditions to which the cable management will routinely be subjected. For outdoor locations, it is advisable to consult the British Galvanisers ‘Corrosion Map of the UK’ which highlights the locations most at risk of accelerated corrosion.
UNDERSTANDING GALVANISED PRODUCTS One of the biggest hurdles to selection of a cable management material that provides the best fit solution for a particular installation is the level of ambiguity surrounding different materials and how they are formed. Over-specification can be costly and the cost increases exponentially with the size of the project. However, under- specification can be equally costly for the client if the installation is not sufficiently robust. Galvanising steel is a cost-effective way of protecting the material, which works
in three ways; firstly, the zinc coating weathers at a very slow rate giving a long and predictable life. Secondly, the zinc coating corrodes preferentially to provide sacrificial protection to any small areas of exposed steel and thirdly, on larger exposed areas, the surrounding zinc prevents ‘creepage’. However, there is often confusion surrounding the terms ‘pre-galvanised’ and ‘hot dipped galvanised’. Pre-galvanised refers to sheet steel that has been through a hot dipped galvanising process at the point of manufacture, with a typical galvanising application of 8-20µm. Hot dipped galvanised products, meanwhile are completely immersed in a bath of zinc after the cable management item has been formed and gain a 55-85µm costing of zinc, making them much more robust and corrosion resistant.
MAKING THE RIGHT CHOICES With a better understanding of galvanisation terminology it is easy to see why pre- galvanised cable management should only be utilised for dry, interior environments and this smooth finish is ideal for exposed cable management installations where the services are on show. Meanwhile, hot dipped galvanised cable management may be more expensive but offers enhanced protection (provided any exposed steel after cutting is coated with a galvanised paint), and can be used for external installations. For more demanding environments, stainless steel is advisable. Stainless steel 304L offers good weldability and is suitable for brewery, dairy, food and pharmaceutical production environments. 316L stainless steel provides even greater corrosion resistance thanks to the addition of molybdenum, and is sometimes referred to as ‘marine grade’. For installations where an extended service
life is required, Corten A steel, which is galvanised after manufacture, provides a suitable solution, with a thicker steel and higher silicon content attracting more zinc in the galvanising bath.
COST VS VALUE Clearly cost and performance have to be considered in tandem, with pre-galvanised and electro-zinc providing the most attractive price point, and hot dipped galvanised cable management typically costing 35-40 per cent more. Stainless steel and Corten silicon rich cable management will cost around 40 per cent more again than hot dipped galvanised. However, all specification decisions should
factor in whole life and installation costs rather than looking at material costs in isolation, taking account of replacement intervals and operational efficiency as part of the material selection strategy.
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42 APRIL 2018 | CABLES & CONNECTORS
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